The present invention relates generally to anion-exchangers for recovering metal values from aqueous solutions, and in particular to crosslinked polyvinylpyridinium anion-exchange resins and their use in recovering anions of radioactive elements such as technetium and plutonium.
As further background, as a consequence of the development and utilization of nuclear fission technologies, large amounts of civilian- and defense-related radioactive nuclear wastes have been and continue to be produced. While some nuclear wastes are handled simply in controlled geological repositories, other waste streams are reprocessed to remove or recover radioactive isotopes. For example, technetium.sup.99 (Tc.sup.99) is a radioactive material which is a fission product of uranium or plutonium used for nuclear fuel. In most aqueous environments, Tc.sup.99 forms a stable anion, known as pertechnetate (TcO.sub.4.sup.-). Pertechnetate is soluble in basic, neutral and acidic aqueous mediums and thus very mobile in a variety of environments. Accordingly, it is critically important in nuclear waste reprocessing strategies, and- in nuclear site remediation, to deal with the mobile pertechnetate ion.
Plutonium also forms stable ions which are desirably recovered in the reprocessing of nuclear waste streams or in the recovery of plutonium from impure scrap materials from plutonium facilities. To date, the two classical methods for recovering technetium and plutonium values have been liquid-liquid extraction and liquid-solid ion-exchange processes. In the field of ion-exchange, one common practice has been to purify plutonium by anionic exchange in nitric acid. As for technetium, the pertechnetate ion exists in acidic, neutral and basic mediums, and thus its associated ion-exchange purifications occur from a wide range of feed materials.
While these ion-exchange processes have generally proven to be operable, ion-exchange resins having greater affinity for ions of plutonium and technetium are needed. The present invention addresses this need.